Deposition of wax, hydrate, asphaltenes and scale during production and transportation of hydrocarbons is causing considerable economic losses to petroleum industries. Moreover, break-through of formation or injection water can also create problems. These economical losses arise through the cost of chemicals, reduced production, equipment failure, and so on. Flow assurance is thus becoming an increasing challenge as depth and step-out distances to new oil and gas fields are increasing in order to exploit more outlying fossil fuel reserves. Systems for monitoring the flow, and to detect and characterize crystallization within the flow and deposition on the pipe wall, are therefore wanted by the industry.
This invention describes a method and apparatus for monitoring and characterizing multiphase flow in a pipeline, with emphasis on characterization of deposit layers and liquid films on the inside wall of a pipeline. The term characterization refers to determining physical properties and thickness of the layer material.
One background prior art reference is Norwegian Application NO19971025 that uses a device for measurement of a coefficient of reflection for high frequency waves in fluids as well as a method for determining water contents in multiphase pipe flow using that device. Another background reference is International Published Application WO2011133046 A1 (related to EP2561339A1 and US20130033272), which describes a method for measuring deposit layers on an inside wall of a pipeline. These inventions are applicable for characterizing the layers close to the pipe wall, but the problem is that these inventions do not assist in determining the layer thickness.
The background Published Application US2010064820 regards measurement of a multiple-phase fluid in a pipe. However, this document discloses a method that requires two sensors for measurement and cannot be used for thicknesses greater than the sensitivity or penetration depth of the largest probe.
Background Issued U.S. Pat. No. 6,198,293 discloses a method and apparatus for thickness measurement using microwaves. However, the method disclosed requires prior knowledge of the permittivity of the material to be measured.
Background Issued U.S. Pat. No. 5,381,694 A describes a method for measuring thickness of ice layers with electromagnetic waves. However, this invention considers ice layers of several wavelengths of thickness.
Finally, reference should also be made to Published Application US 2009/0204346, relating to measurements of a multiphase flow in a pipe.
As illustrated by the references above, known techniques for permittivity measurement of layers are used for either measuring the thickness of the layer by assuming a known layer permittivity or measuring the permittivity of the layer by assuming a known layer thickness. Compared to known techniques for permittivity measurement of layers, the invention makes it possible to determine both layer thickness and layer permittivity.